Housebuilders, building control inspectors and Microgeneration Certification Scheme (MCS) auditors should be alert to the increasing risk that roof-integrated solar mounting systems that use interchangeable solar panels from third-party manufacturers will be installed with solar panels for which the combined system has no fire classification.
Building Regulations and Fire Safety
In the early hours of Sunday morning, Thomas Farriner was awoken by smoke coming under the bedroom door. His bakery downstairs was on fire. It was September 2nd, 1666 and over the next four days this fire would spread, quickly jumping across the narrow lanes from one timber-framed building or thatched roof to another. From its small start in that bakery in Pudding Lane, the Great Fire of London as it became known went on to destroy almost all of the medieval centre of the city.
The Guidance Requires a Fire Classification
Section 12 of Approved Document B deals with roofs, outlining the situations in which roof constructions with varying fire classification can be used. For example, roofing materials with a lower fire classification may only be allowed when installed more than a certain distance from boundaries and with limitations to the maximum area of roof covered.
The resistance of roofs to external fire exposure is measured in terms of penetration through the roof construction and the spread of flame over its surface.
Roof constructions are classified within the European system as BROOF(t4), CROOF(t4), DROOF(t4), EROOF(t4) or FROOF(t4) in accordance with EN 13501-5.
BROOF(t4) indicates the highest performance and FROOF(t4) the lowest, whereas the (t4) indicates the use of Test 4 in the standard.
An alternative route to classification involves testing to a British Standard, BS476-3, with Approved Document B providing a 'transposition table' that allowed a classification to 476-3 to be treated as if equivalent to a given classification to 13501-5.
- If a roof covering does not have a fire classification, it is not possible to follow the guidance in the Approved Document to demonstrate compliance with the building regulations.
- The classification is for the whole roof system, so it is not possible to add fire-resistant layers to an unclassified system and assume a performance – the whole system including the fire-resistant layer must be tested together as a roof build up.
- Building applied PV (on-roof) currently lives in a grey area where a fire classification for the roof without solar panels is assumed to be representative of the classification of the roof with solar installed above it - despite a growing body of evidence that building applied solar does change the fire dynamics of a roof. (See, for example, 1, 2, 3)
- Building integrated PV is not in a grey area – it must have a fire classification to be lawfully used, unless an Alternative Approach is used, requiring a report from a Chartered Fire Engineer for each building the system is used on.
Interaction with the Microgeneration Certification Scheme
The Microgeneration Certification Scheme (MCS) approves and lists both solar panels and solar panel mounting kits. To register a solar installation with the scheme, an MCS certificated solar installation company must use a certificated panel and combine this with a certificated mounting kit.
As a condition of insurance (for example those offered to buyers of new homes by the likes of NHBC, LABC Warranty), many housebuilders require an MCS certificate for the solar installations on their developments.
The MCS12 standard deals with solar mounting kits and it requires that where such kits either replace roof coverings or create excessive gaps in roof coverings that a fire classification to BS EN 13501-5 of BS476-3 is obtained and declared.
Some roof-integrated solar systems are proprietary, combining a dedicated solar panel and mounting kit into a single system whose component parts cannot be interchanged, so that once tested and issued with a fire classification, non-compliant installations are not possible.
Other roof-integrated solar systems consist of a mounting system from one manufacturer that can be interchangeably combined with a solar PV panel from any number of other manufacturers. The MCS12 standard requires that these mounting systems have a fire classification for each solar panel family it can be used with and that these panel families are listed on the MCS12 certificate. A fire rating achieved with one panel family is not portable to another family, even those from the same panel manufacturer, because differences in Bill of Material for different panels have been shown to result in different performances in the fire tests.
The online system of registering an installation with MCS (called the MID) only allows the issue of a certificate if the installation comprises both an MCS certificated panel and an MCS certificated mounting system, but crucially it does not check that the solar panel model used with the mounting system is listed on its MCS12 certificate as having a combined fire classification. This means that it is left to the solar installer to ensure that only listed solar panels are used in combination with the in-roof mounting kit.
- For roof-integrated solar systems that allow interchangeable panels, a loophole in the registration software makes it possible to obtain an MCS certificate for a non-compliant combination of panel and roof-integrated mounting kit for which there is no combined fire classification
- Consequently, the existence of an MCS certificate for roof-integrated solar installation proves neither that the system is compliant with MCS nor meets building regulations.
Recent Difficulties Obtaining New Fire Classifications for Solar PV Systems
In 2023 EN 15725 was updated. This standard deals with the “extended application of fire performance of building products and building elements”. The new version removed the ability of fire test laboratories to use expert judgement to extend fire classifications under EN 13501-5 beyond that which was tested, and instead limited such extended application only to those situations specifically dealt with in the standard.
The new version of EN 15725 did not include extended application guidelines for the fire classification of solar PV roofing systems.
Some fire experts have interpreted that the new version of EN 15725 completely prevents the fire classification of solar roofing, arguing that expert opinion is required to define the test conditions. Other experts believe that testing can still proceed but that a classification can only be issued for the exact system that was tested –in effect limiting the fire classification to a single solar panel model rather than a whole solar panel family with a range of electrical powers as was previously the case.
In September 2023, many of the limited number of test laboratories that are capable of testing withdrew from issuing fire classifications for solar roofing systems, further refusing to test and classify to BS476-3 even though EN15-725 has no direct bearing on this standard.
Hopes were raised that a written opinion from the British Standards Institute (BSI) committee with responsibility for BS476-3 (FSH22-8) would convince reluctant fire testing laboratories to re-open the BS476-3 route to classification, but these subsequently dashed when a change to Approved Document B removed any reference to BS476, leaving only the European classification as a means of compliance with the Building Regulations.Both routes to demonstrating compliance with MCS012 and Building Regulations were closed.
Meantime, the solar industry marches on with its relentless technological progress. New solar panels are constantly being launched and older panels withdrawn from the market. The in-roof solar market is insufficiently large to influence the product strategy of global solar manufacturers, for whom utility scale solar drives the greater part of demand.
Existing fire classifications remain valid, but without a means to test and add new solar panels to their list, the number of products that are still available in the market with which those roof-integrated solar systems that use interchangeable modules have a combined fire classification is diminishing month by month.
Furthermore, the interest of housebuilders in innovations such as Octopus Energy's ‘zero bills homes’ programme has created a pressure to maximise annual solar generation from the roof by using the most up-to-date solar PV panels with the highest power-density (N-Type or TOPcon panels). In almost all cases, these newer panels post-date the withdrawal of testing, so do not have a combined fire classification with the mounting systems.
Confusingly, some of these newer panels have a power output in a smaller size (108 cell) that matches older, larger-area (120 cell) panels for which the roof-integrated system may have a combined fire classification. Solar installers have mistakenly concluded that these newer panels have a fire classification when they do not, by not checking beyond the brand name and power rating to consider whether the actual product code for the panel is listed as having a fire classification.
- The publication of a new version of EN 15-725 in 2023 caused test laboratories to suspend new fire classifications for new PV panel families with roof-integrated solar mounting systems
- The number of products that are still available in the market with which roof-integrated solar systems that use interchangeable modules have a fire classification is diminishing.
- Housebuilders, building control inspectors and MCS auditors should be alert to the rapidly rising risk that roof-integrated solar mounting systems that use interchangeable panels from third party manufacturers will be installed with panels for which they have no fire classification in combination.
- It is insufficient to check that the manufacturer and power level is listed as having a fire classification with such systems – the product code must match – as the classification listed may be for an older panel of the same power, but larger format (area).
How to Get Through This?
The MCS is leading the response to the challenges created by the publication of the new standard and the withdrawal from solar fire classifications by test laboratories.
One possibility, now underway, is to create a industry guidance document for the testing and certification of solar PV roofing systems. The idea is that this document will outline a consistent approach that test laboratories can then use to apply the tests in TS1187 to solar roof samples. It is important that, for it to be widely accepted, the guidance should be developed in consultation with all relevant stakeholders including the solar industry, fire test laboratories, the safety regulators (for all devolved governments) and building control.
The development of this document may require a series of fire tests to demonstrate the approach is rigorous. Given this, and the number of bodies involved it is becoming obvious that this will be no quick fix.
However, you cannot finish what you do not begin, so it is good that there is an agreed approach and that a start has been made.
What Should the Industry do in the Meantime?
Choosing a proprietary roof-integrated solar system that does not allow the interchangeable use of solar panels from different manufacturers greatly reduces the risk, but you should still ask for evidence of the fire classification for the system.
When using a roof-integrated solar system where third party solar panels can be interchangeably substituted, ask the mounting system manufacturer to provide evidence that the exact model of solar panel you intend to use has a UK fire classification (not an indicative classification) in combination with this mounting system, and take steps to ensure that this model is not substituted at any time during the project.
In both cases the MCS012 certificate for the product concerned will have a list of the solar panel product codes with which the system has a fire classification.